Temp sender wire voltage?

[Custom/Ten]

Hey guys what should the voltage read on the green wire to the temp sending unit? My gauge reads low, I have a new thermostat that opens up at 195 as it should, I have a new pcb on the gauge cluster, I have a new temp gauge from lmc and left the resistor off like the directions said to. I have a new sending unit (tu5 dura last) which I read is one of the ones that work on the 67-72s cause apparently some dont work right. The voltage at the green wire is just over 8V. Is that right?this is still as high as the gauge will go.

[Custom/Ten]

When I ground the green wire it won't peg, maybe voltage is low,

[franken]

I'm recalling something more like TU65 sender, but don't trust my memory. I recently read that new sensors are inaccurate.

I'd measure the voltage to ground on the sensor and across the gauge to get an idea of what's happening.

I think most meter movements (the bit that moves the needle) operate on voltage. Based on that, I'd guess the sender is a heat controlled varistor of some sort.

You want to figure out what range of voltage the guage wants and the range of resistance the sender has, then decide how to approach the problem.

[jocko]

Not sure about the voltage - I'm in the middle of going from an aftermarket to a factory tem gauge. TU5 is the correct sender though.

[franken]

Jocko, are you both jocko and Custom/Ten? If not, maybe you should have another thread.

Aftermarket are typically mechanical, and while what is in use now may be right in theory, it seems to not be working, so maybe it's time to start thinking rather than simply randomly swapping parts.

There are different senders based on year, diameter and placement as well. Startlingly, engines get swapped.

[jocko]

Originally Posted by franken

Jocko, are you both jocko and Custom/Ten? If not, maybe you should have another thread.

Aftermarket are typically mechanical, and while what is in use now may be right in theory, it seems to not be working, so maybe it's time to start thinking rather than simply randomly swapping parts.

There are different senders based on year, diameter and placement as well. Startlingly, engines get swapped.

Huh? I already do have another thread, thanks. http://67-72chevytrucks.com/vboard/s...81#post6662681

The aftermarket one I was swapping out was electrical. Well aware of the different thread sizes over the years - the point was to confirm for the OP that he had the correct sender because someone mentioned a different part number that they were not quite sure about. Not really sure what you're saying here.

[Custom/Ten]

Thanks for the replays guys. I just figured some other people might have the same problem and this thread might help them out. I didn't just randomly swap out parts lol. There was a reason for each replacement but don't worry about it ill figure it out.

[BADAZ chevy guy]

The gauge is powered on the other side from the green wire. The green wire is actually a ground wire run through the sending unit which acts like a variable resister. The hotter the sending unit gets, the lower the resistance. The less resistance, the higher the gauge reads. Bypassing the sending unit by grounding the wire should peg the gauge to hot.

[Custom/Ten]

All I want to know is how many volts are supposed to be in the green wire. Mine has 8 volts at the end of the green wire when tested by putting a voltmeter from the end of the green wire to the neg battery post.

[Lee H]

I don't know what it's "supposed" to be, however my 72 C10 reads 8.94 at operating temperature. Another car of the same era reads 9.02 cold. I'm running the wells TU5 in each with factory gauges. At operation temp both read about 2-3 needle widths off the second hash mark from cold. I'd say it's your gauge.

[Avitech]

I just went out and checked mine. I get 8.55 volts with the engine running and the green wire connected to the temp. sender and 12.5 volts with the wire disconnected (engine still running.) My gauge reads tends to stay on the lower end of the green range too, but will climb as the engine heats up in traffic jams and such.

[Custom/Ten]

Ok thanks for the info guys! I didn't expect anyone to go out and check I just figured someone would know. Definitely appreciate it though! Let me know if I can return the favor some time.

[Custom/Ten]

Ok guys i got the gauge to peg!i got some pics, ill show ya what the problem was in case anyone runs into this with the different style lmc temp gauge.

[Custom/Ten]

The lmc gauge does not have a resistor on the back to help hold it in place(the resistor is internal). The top post got grounded against the metal and made it not work right. I made this plastic spacer so this does not happen again.

[Custom/Ten]

[Custom/Ten]

the spacer is on the left in the pic but that's actually the top post.

[Custom/Ten]

These rectangle spacers don't really hold it that good on their own IMO. I feel like this new style gauge should come with a plastic spacer like the one I made but its not really necessary. If your careful you can get it without. I'm just posting this so if anyone's newer style gauge does what mine did in the first pics you can check and see if you screwed up the way I did by accidentally grounding that top post against the metal. Thanks to everyone who posted!

[BADAZ chevy guy]

That's ingenuity at it's finest right there. Good job!